The present invention relates to an optical fiber array device used for optical communication and a method of manufacturing the same, a method of connecting a waveguide of an optical light guide device and an optical fiber of an optical fiber array device with each other, and an optical waveguide module which is formed by connecting an optical fiber array device and an optical waveguide circuit device.
Today, for lower prices an denser circuit integration, the field of optical communication sees progress in xe2x80x94the commercialization of an optical waveguide circuit (PLC; Planer Lightguide Circuit) device in which a plurality of optical waveguides are arranged on a silicon substrate or a quartz substrate. Furthermore, multi-function capabilities required for optical waveguide circuit devices nowadays facilitate higher density integration of optical waveguides to be arranged and large-sized optical waveguide circuit devices.
In general, an optical waveguide circuit device is connected to an optical fiber array device which is formed by arranging optical fibers, and used as a module. FIG. 3 is a perspective view showing a module-type optical device (optical waveguide module) in which an optical fiber array device 7a is connected to the incidence side of an optical waveguide circuit device 8 while an optical fiber array device 7b is connected to the exit side of the optical waveguide circuit device 8.
In FIG. 3, an optical waveguide circuit is formed by an optical waveguide 6 on an optical waveguide substrate 10, whereby the optical waveguide circuit device 8 is formed. The optical waveguide circuit shown in FIG. 3 comprises one incidence-side optical waveguide 6a which branches out through a branch portion 16 such that there are eight optical waveguides 6b on the exit side. The optical waveguide circuit is a splitter-type optical waveguide circuit which divides incident light entering at one optical input part (the incidence side of the incidence-side optical waveguide 6a) and outputs light at eight optical output parts (the exit side of the exit-side optical waveguides 6b). In FIG. 3, an upper glass plate 11 is disposed on the optical waveguide circuit device 8 at the connection terminal surface sides.
The optical fiber array devices 7a and 7b each comprise a guide substrate 1 and a cap plate 4. Although not illustrated in FIG. 3, one or more optical fiber arranging guide grooves for arranging optical fibers 3 are formed in the guide substrates 1. In general, the arranging guide grooves are formed as V-shaped grooves (grooves shaped like a letter xe2x80x9cVxe2x80x9d). As the coating is removed on the connection terminal surface side of the optical fibers, they are inserted in the V-shaped grooves, and the optical fibers 3 inserted in the arranging guide grooves are capped with the cap plates 4.
One optical fiber 3 is fixed to the optical fiber array device 7a which is on the incidence side, while the eight optical fibers 3 are arranged at equal intervals and fixed to the optical fiber array device 7b which is on the exit side. The optical fibers 3 which are fixedly arranged to the optical fiber array device 7b are led from a core wire of an optical fiber tape which is formed by arranging eight optical fibers 3 in parallel in a line at a pitch of 250 xcexcm, of which coating is removed on the connection terminal surface side and inserted respectively in the V-shaped grooves.
The optical fiber 3 which is fixed to the optical fiber array device 7a is connected to the optical waveguide 6a which is disposed on the incidence side to the optical waveguide circuit device 8, while the eight optical fibers 3 which are fixed to the optical fiber array device 7b are connected respectively to the optical waveguides 6b which are disposed on the exit side to the optical waveguide circuit device 8. In general, the arrangement pitch of the optical waveguides 6b is set to 250 xcexcm which is equal to the arrangement pitch of the optical fibers 3 of the optical fiber array device 7b. 
For fabrication of an optical component as shown in FIG. 3, the connection terminal surfaces of respective optical fiber array devices 7a and 7b and the connection terminal surfaces of the optical waveguide circuit device 8 are polished, the connection terminal surface of the optical fiber array device 7a and the connection terminal surfaces of the optical waveguide circuit device 8 on the incidence side are faced towards each other, while the connection terminal surface of the optical fiber array device 7b and the connection terminal surface of the optical waveguide circuit device 8 on the exit side are faced towards each other.
Following this, connection terminal surfaces of the optical fibers 3 which are arranged in the optical fiber array devices 7a and 7b are faced towards the connection terminal surfaces of the optical waveguide 6 disposed at the optical waveguide circuit device 8, and adjusted so as to minimize axial deviations (positional displacements) between the connection terminal surfaces of the optical fibers 3 and the corresponding connection terminal surfaces of the optical waveguide 6. The connection terminal surfaces of respective optical fiber array devices 7a and 7b and the connection terminal surfaces of the optical waveguide circuit device 8 are fixedly adhered to each other with an adhesive or the like which hardens under ultraviolet light (UV).
By the way, as described above, the optical waveguide circuit device 8 has gained more and more functions recently, which has led to the development of the optical waveguide circuit device 8 of a splitter-type which divides light impinging upon one optical input part and outputs light at thirty-two optical output parts or sixty-four optical output parts, for example. Where such an optical waveguide circuit device 8 is to be used as a module-type optical component (optical waveguide module) as shown in FIG. 3, as described above, since the arrangement pitch of the optical waveguides 6b on the exit side of the optical waveguide circuit device 8 is 250 xcexcm, a distance between both edges of the exit-side optical waveguides 6b disposed at the optical waveguide circuit device 8 is 7.75 mm if there are thirty-two optical output parts (optical output ports) and it is 15.75 mm if there are sixty-four optical output parts.
Meanwhile, it is generally known that the optical waveguide circuit device 8 warps because of its manufacturing method. For instance, where the optical waveguide circuit device 8 has thirty-two optical output parts, there are thirty-two optical waveguides 6b on the exit side and the width of the optical waveguide circuit device 8 is 8 mm as shown in FIGS. 4A and 4B, and the optical waveguide circuit device 8 using the optical waveguide substrate 10 of silicon warps to the degree of S which is as much as 2 to 3 xcexcm as shown in FIG. 4A. As shown in FIG. 4B, even the optical waveguide circuit device 8 using the optical waveguide substrate 10 of quartz warps in the degree S of as much as 0.5 to 1.0 xcexcm.
As shown in FIGS. 4A and 4B, the degree of warping S is a value which is expressed by the quantity of a deviation in the direction of height (Y-direction in FIGS. 4A and 4B) between the optical waveguides 6b at the center and the optical waveguides 6b at both ends. The directions of warping are opposite between where the optical waveguide substrate 10 of silicon is used and where the optical waveguide substrate 10 of quartz is used.
The warping prohibits the arrangement of the optical waveguides 6b on the exit side of the optical waveguide circuit device 8 (i.e., an arrangement of the cores at the cross section of the optical waveguide circuit device 8) from presenting a linear shape, but causes the arrangement to have a curved shape in accordance with the warping of the optical waveguide circuit device 8. As the optical fiber array device 7b bearing the optical fibers 3 which are arranged in a linear shape is connected to the optical waveguide circuit device 8, axial deviations are generated between the corresponding optical waveguides 6b and the optical fibers 3. This increases connection loss between the optical waveguides 6b and the optical fibers 3.
To solve this problem, Japanese Laid-Open Patent Publication No. 173043 of 1993 proposes to dispose an external force application mechanism to forcibly curve the optical fiber array device 7 outside the optical fiber array device 7. However, due to the requirement of disposal of the external force application mechanism outside the optical fiber array device 7, this method needs a greater number of parts and components to constitute an apparatus which include this mechanism, is a large-sized apparatus due to the external force application mechanism, and demands laborious fabrication, and hence, has a problem in that the cost is high.
Furthermore, as described earlier, for forming of a module-type optical component (optical waveguide module) by bonding the optical fiber array devices 7a and 7b to the optical waveguide circuit device 8, since an ultraviolet light-hardening adhesive or the like is used to bond the optical fiber array devices 7a and 7b to the optical waveguide circuit device 8, if there is other mechanism disposed externally to the optical fiber array device 7b, ultraviolet light for hardening the ultraviolet light-hardening adhesive is blocked and hence hardening of the ultraviolet light-hardening adhesive is disturbed. This makes it difficult to adhere the optical fiber array device 7b and the optical waveguide circuit device 8 with each other.
In addition, since a material for forming the optical fiber array devices 7a and 7b is different from a material for forming the external force application mechanism according to the proposed method above, as a environmental temperatures where the module-type optical component is used changes, the degree of curvature (the degree of warping) of the optical fiber array device 7b which is curved by the external force application mechanism changes, thereby resulting in a problem that it is not possible to apply an appropriate degree of warping to the optical fiber array device 7b. If thermal expansion coefficient of the forming material of the external force application mechanism becomes large and the degree of warping of the optical fiber array device 7b associated with the change in the environmental temperature accordingly becomes large, a load is applied to the connection portion between the optical fiber array device 7 and the optical waveguide circuit device 8. This causes a problem in that connection loss increases and the connection portion is destroyed.
Moreover, in the recent years, a circuit using slab waveguides has been used widely as an optical waveguide circuit which is formed in the optical waveguide circuit device 8. In a circuit using this type of slab waveguides, optical transmission loss in light from slab waveguides at both ends is larger than that in light from slab waveguides at around the center. Hence, when a plurality of respective waveguides on the output side of the slab waveguides are connected to the corresponding optical fibers of the optical fiber array device 7, levels of optical power outputted at respective optical fibers become different from each other, which in turn makes it impossible to execute appropriate signal processing. Due to this, if the levels of the optical power outputted at respective output terminals become different from each other as described above, it is necessary to dispose attenuators for respective output terminals such that all levels of optical power become uniform, which requires a large size and a high cost.
The present invention has been made to solve the problems described above in the conventional techniques. Accordingly, a first object of the present invention is to provide an optical fiber array device which can be connected with an optical waveguide circuit device, which is a connection receiver, at a low connection loss even despite changes in temperature in an environment where the optical fiber array device is used, and which is easily manufactured in a small size at an inexpensive cost, and to provide a method of manufacturing such an optical fiber array device. A second object is to provide a method of connecting a plurality of arranged optical waveguides and optical fibers of an optical fiber array device with each other, and to provide an optical waveguide module using the connection method, with which it is possible to ensure uniform output power at respective optical fibers without using attenuators or other optical components even when the optical fibers are connected to such optical waveguides among which both ends have a greater optical transmission loss than the ones at the central ones as in an optical circuit which comprises slab waveguides as described above.
To achieve the objects above, the present invention provides an optical fiber array device and a method of manufacturing the same, at the same time, a method of connecting the optical waveguides of an optical waveguide circuit device to optical fibers of an optical fiber array device, and an optical waveguide module using the connection method thereof.
That is, an optical fiber array device according to an embodiment of the present invention comprises a guide substrate in which a plurality of optical fiber arranging guide grooves are formed and a cap plate which caps optical fibers which are inserted in the arranging guide grooves, wherein warping is created in the optical fiber array device in the direction of an arrangement of the optical fibers and a shape of the arrangement of the optical fibers at least at the connection terminal surfaces is curved-shaped because of the warping.
Furthermore, in an optical fiber array device according to a different embodiment of the present invention, in addition to the structure above, warping is created in the optical fiber array device in accordance with the warping of an optical waveguide circuit device such that connection terminal surfaces of the optical waveguide circuit device approximately match with connection terminal surfaces of the corresponding optical fibers when respective connection terminal surfaces of the plurality of optical fibers which are arranged in the optical fiber array device are faced towards respective connection terminal surfaces of the plurality of optical waveguides which are arranged in the optical waveguide circuit device at the side of the connection receiver of the optical fiber array device.
A method of manufacturing an optical fiber array device according to the present invention is a manufacturing method of the optical fiber array device as described above, and is characterized in creating warping in the optical fiber array device by means of a contraction stress which occurs during hardening of an adhesive which bonds the guide substrate and the cap plate with each other.
Furthermore, the method of manufacturing an optical fiber array device according to the present invention, in another aspect, requires bonding of the guide substrate and the cap plate to each other as they are curved due to an external force to thereby create warping in the optical fiber array device by means of the external force and the contraction stress which occurs during hardening of the adhesive.
Furthermore, the present invention provides the following structure as a method of connecting an optical waveguide circuit device which warps in a curved shape and an optical fiber array device with each other. More precisely, it is a method of connecting optical waveguides and optical fibers with each other, according to which the plurality of optical waveguides, which have approximately the same transmission losses and which are disposed in parallel to each other in an optical waveguide circuit device which warps in a curved shape, wherein the optical connection is simultaneously carried out with the plurality of optical fibers which are disposed in parallel to each other in an optical fiber array device, such method being characterized in that the optical fiber array device has warping which approximately matches with the curved shape of the optical waveguide circuit device and that the optical connection between the optical waveguides and the corresponding optical fibers is simultaneously carried out such that axial deviations between the optical waveguides and the corresponding optical fibers are small when a connection terminal surface of the optical waveguide circuit device which has the curved shape is faced towards a connection terminal surface of the optical fiber array device.
In the present invention of the structure as above, the optical fiber array device comprises a guide substrate in which a plurality of optical fiber arranging guide grooves are formed and a cap plate which caps the optical fibers which are inserted in the arranging guide grooves, and a contraction stress which occurs during hardening of an adhesive which bonds the guide substrate and the cap plate with each other, for example, creates warping in the optical fiber array device in the direction of an arrangement of the optical fibers.
It is generally known that the optical waveguide circuit device, at the side of the connection receiver of the optical fiber array device, warps because of the manufacturing method of the optical waveguide circuit device. According to the present invention, since the shape of the arrangement of the optical fibers arranged in the optical fiber array device is formed in a curved shape, at least on the connection terminal surface side, by the warping in the direction of the arrangement of the optical fibers, when the optical waveguide circuit device and the optical fiber array device are connected to each other, connection terminal surfaces of the optical waveguides arranged in the optical waveguide circuit device are easily aligned to connection terminal surfaces of the optical fibers arranged in the optical fiber array device.
As warping is created in the optical fiber array device in accordance with the warping of the optical waveguide circuit device such that the connection terminal surfaces of the optical waveguides and the connection terminal surfaces of the corresponding optical fibers approximately match with each other when the connection terminal surfaces of the optical fibers of the optical fiber array device are faced with the connection terminal surfaces of the optical waveguides of the optical waveguide circuit device, it is possible to match the connection terminal surfaces of the optical waveguides and the connection terminal surfaces of the corresponding optical fibers with each other, and hence, to connect the optical waveguides and the corresponding optical fibers with each other at a very low connection loss.
Furthermore, according to the present invention, since the warping of the optical fiber array device is created by the contraction stress which occurs during hardening of the adhesive which bonds the guide substrate and the cap plate to each other, fabrication is easy. Unlike where an external force application mechanism is disposed, there is no change in the degree of warping of the optical fiber array device due to expansion or the like caused by heating of the external force application mechanism in accordance with environmental temperatures where the device is used, which in turns allows the maintenance of a low connection loss between the optical fiber array device and the optical waveguide circuit device. This does not lead to an increase in the size or complexity of an apparatus, or an increase in cost, etc.
Furthermore, where the guide substrate and the cap plate are bonded with each other as they are curved due to an external force, if warping is formed in the optical fiber array device by the external force and the contraction stress occurring during hardening of the adhesive, application of an external force in the same direction with the contraction stress of the adhesive increases the warp-induced distortion. On the contrary, application of an external force in the opposite direction to the contraction stress of the adhesive decreases the warp-induced distortion. In this manner, it is possible to adjust the degree of warping by means of adjustment of the contraction stress of the adhesive and the external force.
Furthermore, the present invention provides a method of connecting optical waveguides and optical fibers having the following structure. More precisely, it is a method of connecting optical waveguides and optical fibers with each other, according to which three or more optical waveguides disposed in parallel on an optical waveguide circuit device and among which ones at both ends have a greater optical transmission loss than the central ones, and three or more optical fibers disposed in parallel on an optical fiber array device, wherein the optical connection is simultaneously carried out. Such method being characterized in that at least either one of the parallel optical waveguides or the parallel optical fibers are disposed in parallel such that an axial deviation in the direction perpendicular to the direction of the arrangement increases toward the center of the arrangement from both ends of the parallel disposal arrangement. After such a method, connection terminal surfaces of the optical waveguides and connection terminal surfaces of the corresponding optical fibers are faced with each other such that an axial deviation in the direction perpendicular to the direction of the arrangement increases toward the center of the arrangement, thereby optical connection of the optical waveguides and the corresponding optical fibers is simultaneously carried out.
One of the preferred methods of the optical connection requires the warping of at least either one of the optical waveguide circuit device or the optical fiber array device in the direction perpendicular to the direction of the arrangement of the optical waveguides or the optical fibers, so that at least either one of the parallel optical waveguides or the parallel optical fibers are arranged to ensure that an axial deviation in the direction perpendicular to the direction of the arrangement increases toward the center of the arrangement from both ends of the parallel disposal arrangement.
Furthermore, another method of the optical connection according to the present invention is a method of connecting optical waveguides and optical fibers with each other, according to which three or more optical waveguides disposed in parallel to an optical waveguide circuit device and among which the ones at both ends have a greater optical transmission loss than the central ones, wherein the optical connection is simultaneously carried out with three or more optical fibers which are disposed in parallel to each other in an optical fiber array device. Such method being characterized in that at least either one of a parallel disposal pitch of connection terminal surfaces of the optical waveguides or a parallel disposal pitch of connection terminal surfaces of the optical fibers is uneven, after the optical waveguides and the corresponding optical fibers are faced towards each other such that a degree of deviation between the positions of the connection terminal surfaces of the optical waveguides and the positions of the connection terminal surfaces of the optical fibers increases toward the center of the optical waveguides and the optical fibers disposed in parallel, thereby the optical connection is simultaneously carried out.
Furthermore, the present invention provides an optical waveguide module having the following structure. That is, it is an optical waveguide module which is formed by connecting three or more optical waveguides disposed in parallel to each other in an optical waveguide circuit device, with three or more optical fibers disposed in parallel to each other in an optical fiber array device, such that connection loss increases toward the center from both ends in the direction of the parallel disposal of the optical waveguides or the optical fibers, wherein the optical waveguides of the optical waveguide circuit device are formed such that an optical transmission loss is larger toward both ends from the center of the arrangement of the optical waveguides of the optical waveguide circuit device, and where a loss value combining an optical transmission loss at each optical waveguide with a connection loss with each associated optical fiber is the total loss of a connected pair of each optical waveguide and each associated optical fiber, a difference between the maximum value and the minimum value among the total losses of respective connected pairs is smaller than a difference between the maximum value and the minimum value among the optical transmission losses of the optical waveguides which are disposed in parallel to each other. The difference between the maximum value and the minimum value among the total losses of respective connected pairs of the optical waveguides and the optical fibers is preferably zero.
In the connection method above according to the present invention, first, at least either one of the parallel optical waveguides or the parallel optical fibers are disposed in parallel such that an axial deviation in the direction perpendicular to the direction of the parallel disposal arrangement increases toward the center of the parallel disposal arrangement from both ends of the parallel disposal arrangement or such that at least either one of the parallel disposal pitch of the connection terminal surfaces of the optical waveguides or the parallel disposal pitch of the connection terminal surfaces of the optical fibers is uneven. Therefore, the connection terminal surfaces of the optical waveguides and the corresponding optical fibers are faced toward each other such that deviation increases toward the center of the parallel disposal arrangement, thereby the optical connection is simultaneously carried out.
By the way, while the optical waveguide circuit device which comprises three or more optical waveguides which are disposed in parallel to each other may be a branch optical splitter using slab waveguides, an array waveguide-type diffraction grating, etc., in such an optical waveguide circuit device, optical waveguides at both ends of the parallel disposal arrangement in the optical waveguide circuit device have a larger optical transmission loss than the optical waveguides at around the center of the arrangement.
Hence, where such an optical waveguide circuit device is to be connected to an optical fiber array device, according to the present invention, which requires as described above, facing of the optical waveguides and the corresponding optical fibers towards each other such that deviation between the optical waveguides and the corresponding optical fibers increases toward the center of the optical waveguides and the optical fibers disposed in parallel, thereby simultaneously carrying out the optical connection between the optical waveguides and the optical fibers, making it possible to increase connection loss between the optical waveguides and the corresponding optical fibers toward the center of the optical waveguides or the arranged optical fibers.
Hence, since the optical fiber array device is connected using the connection method as described above to the optical waveguide circuit device, such as a branch optical splitter and an array waveguide-type diffraction grating formed such that optical waveguides at both ends of the parallel disposal of the optical waveguides in the optical waveguide circuit device have a larger optical transmission loss than the optical waveguides at around the center of the parallel disposal of the optical waveguides, it is possible to ensure that a difference between the maximum value and the minimum value among values (total losses of the connected pairs), which combine optical transmission losses of the optical waveguides with connection losses with the corresponding optical fibers, is smaller than a difference between the maximum value and the minimum value among the optical transmission losses of the optical waveguides.
Furthermore, in the connection method according to the present invention, the difference between the maximum value and the minimum value among the total losses of the connected pairs of the optical waveguides and the optical fibers is approximately zero, if the connection above is realized after parallel disposal positions of the optical waveguides for the optical waveguides which are to be disposed in parallel to each other to the optical waveguide circuit device and parallel disposal of the optical fibers positions for the optical fibers which are to be disposed in parallel to each other to the optical fiber array device are formed such that relative positions between the optical waveguides and the optical fibers connection receivers to the other, as they are faced with each other have appropriate values which allow to offset differences between the optical transmission losses due to the different parallel disposal of the optical waveguides positions of the optical waveguides.
Hence, application of the connection method according to the present invention eliminates the necessity to insert attenuators or the like as in the prior arts. This realizes a smaller size and lower cost of an optical waveguide module which is formed by connecting the optical waveguide circuit device and the optical fiber array device with each other.
Furthermore, during the stage of connecting the optical waveguide and the optical fibers with each other, as at least one of the optical waveguide circuit device and the optical fiber array device is curved in the direction perpendicular to the direction of the arrangement of the optical waveguides or the optical fibers, it is possible to dispose the optical waveguides and the optical fibers in parallel very easily in a manner in which at least either one of the parallel optical waveguides or the parallel optical fibers are disposed in parallel such that an axial deviation in the direction perpendicular to the direction of the arrangement increases toward the center of the parallel disposal arrangement from both ends of the parallel disposal arrangement.
Furthermore, with respect to the optical waveguide module according to the present invention, in order to form the optical waveguide module according to the present invention using the connection method above, it is possible to ensure that the difference between the maximum value and the minimum value among the total losses of the connected pairs of the optical waveguides and the optical fibers is zero, for example, which is therefore smaller than the difference between the maximum value and the minimum value among the optical transmission losses of the optical waveguides. This realizes an optical waveguide module of a small size at a low cost, in which optical intensities outputted at a plurality of output terminals are approximately equal to each other, without disposing attenuators or the like.